1. Field of the Invention
The present invention relates to the rollers of a peristaltic pump rotor which is used for the administration of enteral and/or parenteral solutions to a patient. More particularly, the present invention relates to rollers which provides decreased current draw, while ensuring precise volume measurement as the peristaltic pump rotor rotates.
2. State of the Art
The use of peristaltic pumps and infusion sets to administer solutions to patients is well known in the medical arts. Pumps and infusion sets are used for both enteral and parenteral applications. Enteral feeding pumps are used to provide patients with nutrition and medication when they are unable, for a variety of reasons, to eat normally. Parenteral (intravenous) pumps are used to provide solutions to ensure adequate hydration and to provide needed nutrients, minerals and medication directly into the blood stream of the patient.
The rate at which the solution enters the body can be controlled in a variety of different ways. With parenteral applications, it is not uncommon for the infusion set to be placed in a free standing arrangement so that gravity helps force the solution into the patient. The rate at which the solution enters the patient also can be roughly controlled by various clamps, such as roller clamps, which are currently available on the market.
In many applications, however, it is necessary to precisely control or monitor the amount of solution which enters the patient. When this is the case, a regulating device, such as an enteral feeding pump or a parenteral infusion pump, is placed along the infusion set to control the rate at which the solution is fed to the patient. In applications where a pump is used, the clamps used to regulate flow are typically opened to their fullest extent to prevent the clamp from interfering with the proper functioning of the pump. The clamp is opened with the expectation that the enteral feeding pump will control fluid flow through the infusion set.
Enteral and parenteral pumps are desirable because they enable precise control over the solution flow rate. This can be accomplished with a variety of pumping mechanisms.
One common pump is a peristaltic pump in which a rotor is provided with a plurality of rollers (typically three). The rollers engages a flexible tube which is wrapped around the rotor in a U-shape. As the rotor turns, the tube is selectively pinched off between adjacent rollers to form a section of the tube with a predetermined amount of solution. Each partial rotation of the rotor, causes the predetermined amount of solution to be moved from the upstream side to the downstream side of the tube. By tracking the number of rotations (or partial rotations) of the rotor, the amount of solution delivered can be determined with a high degree of accuracy.
The use of such rotors has greatly improved the mobility of patients who must use enteral or parenteral pumps. Pumps which use rotors and other flow measuring devices to confirm delivery rates are described in U.S. Pat. Nos. 5,514,102 and 5,531,680.
Prior to the development of mobile pumps such as those described in the above-referenced patents, patients who used enteral feeding pumps and the like were often hooked to a pole which carried their enteral feeding solution. While receiving medication or nutrient solution, the patient would be limited in mobility to wherever the pole could be moved. The inventions described in the above-referenced patents have increasingly enabled patients to use portable pumps which operate on batteries. This enables many patients to enjoy activities such as camping and hiking that were previously very difficult, if not impossible.
One continual concern with portable enteral feeding pumps and other types of peristaltic pumps is the amount of current consumed. Those skilled in the art will appreciate that the amount of current draw directly effects the battery life, and thus the amount of time which a patient can use the pump without requiring a recharge. If the current draw can be reduced, the pump will be able to operate longer on a given charge and enable the patient to participate in camping and other activities on a more prolonged basis.
One mechanism for decreasing current draw is to increase the radius of the roller on the rotor. The increased radius provides a larger moment arm and reduces the current required to operate the rotor. Increasing the radius of the roller, however, raises the problem of sealing the tube segments. If the roller gets much larger in diameter than those commonly used (i.e. 0.215 inches in diameter), it becomes increasingly difficult to collapse the tube to define a discreet segment. Without discreet segments being formed in the tube, it becomes very difficult to determine the amount of liquid which actually flows through with each rotation. While there are mechanisms which will enable such determination, they are generally costly and may interfere with portability of the pump. Thus, rotor rollers have generally been between 0.15 and 0.30 inches in diameter when used with a xc2xc inch outside diameter tube.
Thus, there is a need for a roller and a method of using a roller which reduces current draw, but which does not interfere with accurate flow determination. Such a roller should be easy to use and should not otherwise interfere with operation of the pump.
Thus, it is an object of the present invention to provide an improved roller for peristaltic pumps.
It is another object of the present invention to provide such a roller which decreases current draw in an enteral or parenteral pump.
It is yet another object of the present invention to provide such a roller which does not interfere with determination of fluid flow through the pump.
The above and other objects of the invention are realized in specific illustrated embodiments of an improved roller for peristaltic pumps. The roller has a central portion configured for rotation, and a second portion which projects from the central portion.
In accordance with one aspect of the invention, the roller has a plurality of projections which extend outwardly from the central section. The projections are positioned to engage the flexible tube wrapped around the rollers. The projections allow a roller of larger overall diameter to still pinch off the flexible tube into discreet segments.
In accordance with another aspect of the invention, the roller is formed with a plurality of outwardly extending arms to provide an increased effective radius, and a sharper radius to pinch off and thus seal the flexible tube. Because of the spacing between the ends of the arms, however, the roller is able to pinch off the flexible tube which is wrapped around the rotor.
While described herein as projections, those skilled in the art will appreciate that the roller could be made of a larger diameter and then have portions cut out or otherwise removed to leave a non-circular circumference. As used herein, references to projections are intended to include protrusions which are left on such a roller.